I had the strangest dream last night. I was giving a seminar one hundred years in the future and everyone was laughing, albeit discretely, at my amazing naiveté. Every time I'd present a fact, I'd see condescending smiles and head-shakes, until I cried out, “Hey, some of this must still be true!” More head-shakes. “Oh come on! DNA is the genetic material, I know that!”.

“Oh Mole”, chuckled the Chair, “DNA is a genetic material, but most of the interesting heredity is based on multidimensional lipid interfaces - surely you must have had an inkling of that in your own time? Here's how it works...” and then I woke up.

One hundred or so years ago we knew a lot, and there was a lot we didn't know. Now we know more. It is tempting to view this acquisition of knowledge as a bag of chips. There's information to eat away at, and when the bag is empty we'll know it all. Sometimes we have to put one or two chips back when we get something a bit wrong, but mostly we are working our way through the bag.

But the reality is that we generally think we know much more than we do, because much of what we take as true simply isn't. Our understanding turns out to be superficial. And the really frustrating thing is that we really can't predict what will or won't be `true' in the future. In the best cases, we have an approximation of the truth that can be refined with time, but too often we just have to throw away the bag and start a fresh one.

It's easiest to see how this happens through the lens of history, but too easy to write that off with smiles and head-shakes at how naive people were back then. Such `knowledge' can be insidious, and it reaches into our society even in the face of new `facts'.

One hundred or so years ago, we didn't have a clear idea of how genetics works, but we knew a number of `truths' about it. Mendel had done his studies decades before, but these went largely ignored - not because they weren't communicated (this is revisionist history to explain why we didn't all know it was true), but because they didn't fit the `facts'. For example, there was nothing in Mendel's work that could explain the fact of telegony.

Telegony is the effect of a previous mating on subsequent progeny, independently of the current sire. A little over one hundred years ago, it was a `fact'. Not a hypothesis, not a theory, but a fact. It was not only supported by data, but so obviously true that any theory of heredity would have to account for it. For example, concepts involving a `mixing of the blood' upon mating would do nicely. It is argued that Darwin's hypothesis of `pangenesis' (blending of characteristics) was based in part on telegony.

Why was telegony so widely accepted? The evidence came partly from studies of heredity in plants where the phenomenon can apparently exist, since some plants store pollen grains for future use. Then there was the oft-told story of Lord Morton's mare. In the early 1800s, Lord Morton undertook a breeding program to rescue the near-extinct quagga, a horse with striped legs and a stiff mane. He bred a male quagga to a chestnut mare and produced a hybrid. Subsequently, he reportedly bred the mare to a black Arab stallion, and all the foals had stripes on their legs: quagga stripes. Irrefutable evidence that telegony was real.

Of course it was real. A female that had been `contaminated' by a male would be forever contaminated; one had only to look at the world around to see that it was certainly true. Society was drenched in this truth. Blood tells.

Obviously, this is all bullstuff and, in the early 20th century, experimental truth triumphed over what many might have wished to be true. But this sort of thinking pervades our society even now - just google `telegony'. More to the point, it intrudes on lives in strange ways that we can't quite equate with science, but perhaps we should. Take dog breeding.

Long before we understood dog genetics, there were those who bred these animals, selecting certain traits, with the goal of breeding these true. The practice continues to this day, because it works. Except for one little thing. If you happen to have a champion bitch, and she happens to have a bit of afternoon delight with the mongrel next door, then she will immediately and irrevocably lose her champion status forever. Because the blood line has been contaminated.

I didn't believe this myself so I called the local kennel club, where a very nice woman assured me that of course she would lose her status if this were to happen and this is standard in dog-breeding circles the world over. We talked some more, and it quickly became clear that she fully understood basic animal husbandry and genetics, and she entirely took my point that there was no scientific basis for the kennel club's rules. Except, of course, that you can't contaminate the blood line.

A call to the National Shepherder's Association got me a more curt but equally committed response. I suspect that the same would be true of official associations for the breeding of chickens, pigs, horses, cows and English royalty.

Here's my point. Telegony was `true' - and important enough to ignore Mendel and others who were on the right track. It fit fundamental notions of the society in which it was studied, and its echoes continue in our society today.

Whenever you do an experiment that is based on a set of ideas that you hold as true, or probably true, you run the risk of building on a foundation of sand, no matter how solid it feels. When was the last time you questioned your assumptions? When did you last critically read the papers on which these assumptions are based and challenge them? Have you ever read them?

Okazaki's famous fragments might be artefacts of repair mechanisms for the removal of modified nucleotides. Hershey and Chase's measurements on the molecular basis of inheritance showed deviations in excess of the amounts of protein or nucleic acid that would probably have contaminated their preparations. And DNA is only a mechanism for heredity. Maybe.

If you want certainty, get religion. Science, I'm afraid, is like living on a beach. Sometimes its firm and hard and you can build a house, but then the waves come and it all washes away. So we build again, and all the time we're learning. But we have to be fully aware that even our most fundamental assumptions can be wrong - or not entirely right (which might be the same thing). Is Newtonian mechanics generally right and only sometimes wrong, or is it entirely wrong and only sometimes seems right? (Hopefully you know why Newtonian mechanics gets this grief; if not, you either need a refresher in physics or maybe you're reading this when you should be doing your homework?)

All of this impacts on our science every day (except when we sit in committee meetings from dawn till dusk). Most of us tend to do experiments that add a bit to the heap, confirming this or that side of the story, all assuming that we're on fairly solid ground because we don't question any of the foundations. Sure, we could waste a lot of time questioning foundations that are solid and right, but maybe it might do to look for the weak spots? A good tug at the right place can sometimes produce extremely entertaining results.

So, in the end, it comes to this: how do we know what we know? Science. The scientific method is not only a way to get papers published (well...). It's a way to know things. Yes, it's built on sand, but it stands firmer (for my money) than any other foundation I know, in part because we're able to let bits of it fall. And that's, perhaps, where the strength lies. We tug and pull and test our knowledge. If we're good, we pull down the parts that don't hold up. The parts that stay up? We know.

Do you agree? I'll tell you why you shouldn't. Nobody should. This isn't just philosophical rumblings, it's a matter of life and death. Let's go for a walk on the beach and I'll tell you why.

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Have you seen our First Person interviews with the early-career first authors of our papers? The authors talk about their work in and out of the lab, the journeys that led them to where they are now and the scientists who inspired them along the way. Recently, we caught up with first authors Zhe-Long Jin, Cathy Cheng, Yuqing Xia, Ning Huang and Claudio Bussi.

Did you know The Company of Biologists invites applications from the organisers of a range of charitable activities, including meetings, workshops and conferences, in the fields covered by our journals? The next deadline for grant applications is 4 January.

The second in our series of cell dynamics meetings now turns to organelles. This May 2019 meeting in Lisbon, Portugal, aims to bring together scientists studying the interface between organelles and the cytoskeleton at different scales and perspectives using a range of model systems. Find out more and apply for your place here.

Do you have a paper with reviews from another journal that you’d like to submit to Journal of Cell Science? We will fast-track your paper and give you an initial decision within a week. Find out more here.